The present invention relates to a method and apparatus for co-processing hazardous wastes.
Many industrial furnaces use burners for combustion of fuel with air to produce a high temperature flame which is used as an energy source for heating, melting and other industrial processes. These industrial furnaces often provide retention time at temperatures which are compatible with conditions desired for decontamination of hazardous components exhausted from different industrial processes and from primary incinerating chambers of industrial and/or hazardous waste incinerators. In addition, many industrial furnaces are equipped with bag houses and scrubbers to clean the exhaust gases after thermal treatment to remove hazardous constituents.
Historically, industrial furnaces, and particularly cement kilns, have been used to co-process waste fuel streams which are fed into the furnace to provide part of the heat required for the process. Any inorganic components of the waste fuel stream are discharged as components of the exhaust gases or become mixed with the product produced within the industrial furnace. This contamination of the products produced in industrial co-processing furnaces limits the volume and chemical composition of wastes which can be processed in this manner. Slagging combustion chambers have been attached to industrial boilers to permit some liquid waste containing a small amount of inorganics to be incinerated. Hot combustion product generated from the burning of liquid wastes are separated from inorganic residue in these slagging combustion chambers prior to the hot gases being discharged into industrial boilers through a dedicated opening in the boiler wall. This provides for the heat released from such burning to be recovered in the boiler and for the inorganic residue stream to be slagged and discharged from the slagging combustor, thereby preventing significant introduction of inorganic ash into the boiler. In cement kilns and large boilers. Liquid fuel is typically mixed with clean fuel prior to burning and homogenized to insure a consistent caloric value, viscosity and other characteristics. Solid high BTU wastes, such as automobile tires, may also be co-processed after they are shredded and injected into furnaces which are designed to burn solid fuels. The technologies described above have been designed to use a portion of the heat made available from the burning of a waste stream inside of the co-processing industrial furnace. This heat recovery permits a reduction in the firing of expensive clean fuel which would be required to maintain the industrial process.
Significant effort is now being expended on the treatment of solid wastes, such as contaminated soils, from sites such as leaking underground storage tanks. A significant portion of this decontamination will be accomplished by treating soil in portable or stationary incinerating chambers. The remediation of this contaminated soil can be accomplished with significantly less expense if existing industrial furnaces can be used to co-process such wastes.
Presently methods and apparatus for co-processing wastes are not suitably designed to process solid wastes. These wastes cannot be charged into industrial furnaces without upsetting the quality of the products being produced due to their low caloric value and the large volumes of residues which remain after decontamination. Currently, several attempts have been made to modernize existing cement kilns to accept contaminated flue gases delivered by a dedicated flue duct which directs these flue gases to the cement kiln. These contaminated flue gases are fumes derived from an auxiliary incinerating chamber designed as a rotary kiln to treat contaminated soil by a fuel/air burner firing inside of the rotary kiln.
Problems exist, however, with the ability of such cement kilns to accept contaminated flue gases. These cement kilns have exhibited a decline in the quality of the products produced, a decrease in heating efficiency, a loss of control over the levels of excess oxygen and combustibles at the kiln exhaust, and poor temperature distribution inside of the kiln. Such problems have made the presently known approach economically unattractive and environmentally risky for the treatment of the majority of hazardous wastes